Despite being a newly-elected MP, he enlisted in the military, served for four years, and saw action in France during World War II.

Harris became a casualty and lost his seat in the 1957 election that brought John Diefenbaker to power.

In 1958, he attempted a move to provincial politics and ran for the leadership of the Ontario Liberal Party.

Following his defeat, Harris retired from politics and returned to his law practice.

[1] The public library in Markdale, Ontario, is named after Walter Harris.